1. Field of the Invention
The invention is related to the field of valves, and more particularly, to a lift axle control valve.
2. Description of the Prior Art
Lift axles are commonly used on heavy vehicles, such as trucks. They are used to bear weight when the vehicle is loaded and then can be lifted when unloaded. The lift axle is therefore used as needed.
The lift axle can be deployed to avoid exceeding weight limits when the vehicle is loaded. But when the lift axle is lifted or retracted, its wheels disengage from the road or other ground surface and no longer assist in the bearing of weight. When the load weight of the vehicle is less than the load capacity of the primary axles, the lift axle suspension may be raised to avoid extra wear on the lift axle and tires. Operating the vehicle with the lift axle suspension raised can also improve fuel economy, traction, and maneuverability. In addition, when the vehicle is driven in reverse, the positive castor angle of the lift axle wheels may hinder self-steering and cause excess wear to the tires. Raising the lift axle disengages the wheels from the ground, thereby avoiding these issues.
Many heavy vehicles include a pneumatic air system. Therefore, it is advantageous to use pneumatic air to both lift up and to move down and deploy a lift axle. When down, a load pressure is used to force the lift axle downward and bear a portion of the weight of the vehicle.
Heavy vehicles often use pneumatic air in a suspension system, where air springs are inflated in order to lift the vehicle and maintain a vehicle suspension height during operation. The pressure of the air being provided to such a pneumatic suspension system can be controlled in order to provide proper suspension height and proper suspension performance. The suspension or load air pressure can therefore be controlled in order to control ride performance.
One controlled ride performance characteristic is the ride height, which can be the amount of suspension element extension or can be the height of the vehicle frame from the suspension. Ride height can be controlled according to a loaded vehicle weight, a road roughness, etc. The ride height will determine the amount or range of movement of the suspension and can affect vehicle braking, cornering, ride roughness, load leveling, etc. Therefore, it is common practice to regulate the suspension air pressure in order to control the ride and handling of the vehicle.
Increased awareness of safety issues, and highway wear due to heavily loaded vehicles, has led to jurisdictions where lift axle loading is becoming regulated by governmental entities. The aim is to have lift axles be substantially equally loaded with the other non-lift axles of a vehicle. Excessive load bearing by a lift axle may cause poor braking and/or steering by the vehicle. Further, excessive load bearing by one axle of a vehicle will cause uneven or excessive road wear.